This invention relates generally to the field of process measurement and more specifically to a method and system for detecting hidden edges.
The importance of precise real-time measurements for the assembly and inspection of aircraft, buildings, and other structures has led to the demand for precision edge location systems. When assembling or inspecting a structure, one may need to know the location of the edge of a part, which may often be covered and not visible. Known methods for locating hidden edges, however, have not been satisfactory with respect to effectiveness, precision, and flexibility.
One known method for detecting edges uses feeler gauges. A feeler gauge measures the position of an edge by determining the position where the gauge comes in contact with the edge. A problem with the feeler gauge method is that it is time-consuming. To measure an edge, the feeler gauge is moved slowly to the edge and measures the edge. After measuring the edge, the feeler gauge is moved away from the edge and moved to the next edge to be measured. The feeler gauge cannot perform the measurements using one continuous movement. Additionally, since the feeler gauge must come into contact with the edge, the gauge cannot be used to detect hidden edges.
One known method for detecting hidden edges uses x-ray imaging. An emitter is placed at one surface of an object, and a detector is placed at the opposite surface to collect radiation that has passed through the object. The collected radiation forms an image of edges not visible from the surface. One problem with this method is that it requires access to opposite surfaces of an object, which is often not possible. Also, it is often difficult to place an emitter on one side of an object and a detector at the opposite side of the object. Additionally, developing a final image of the hidden edges may be a lengthy process. Another known method for detecting hidden edges uses eddy-current probes. An eddy-current probe detects changes in voltages as the probe is moved across an object with hidden edges. The voltage rises as the probe moves from a thinner region to a thicker region. A problem with this method is that it is not accurate. The voltage signal is affected by many factors that degrade the accuracy and precision of the probe, for example, the object""s composition, thickness, and electrical properties. Additionally, the eddy-current probe can only detect hidden edges in conductive materials.
A backscatter gauge as described in U.S. Pat. No. 5,666,394 to Swanson may be used to measure the thickness of an object. To measure the thickness of an object, the backscatter gauge directs radiation towards the object, detects reflected radiation, and associates the reflected radiation with a thickness. A problem with this method is that the gauge requires the generation of calibration curves. The backscatter gauge must first determine the reflected radiation from an object of known thickness to generate calibration curves. The backscatter gauge then uses the calibration curves to determine the thickness of objects of unknown thickness.
While these devices and methods have provided a significant improvement over prior approaches, the challenges in the field of quality assurance has continued to increase with demands for more and better techniques having greater effectiveness, precision, and flexibility. Therefore, a need has arisen for a new method and system for detecting hidden edges.
In accordance with the present invention, a method and system for detecting hidden edges is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods.
According to one embodiment of the present invention, a system for detecting hidden edges is disclosed. The system comprises a workpiece having a surface and a hidden edge located below the surface. A radiation source moves along the workpiece surface and generates radiation. A radiation receiver moves along the workpiece surface and receives reflected radiation. A processor coupled to the radiation receiver determines a count rate of the reflected radiation, determines a change of the count rate corresponding to the hidden edge, and associates the change to a position on the workpiece surface. More specifically, the processor determines a position of a centroid associated with the change of the count rate, and the position of the centroid corresponds to the position on the workpiece surface.
According to one embodiment of the present invention, a method for detecting hidden edges is disclosed. Step one calls for providing a workpiece having a surface and a hidden edge located below the surface. Step two provides for directing radiation towards the workpiece surface with a radiation source. At step three, the method provides for receiving reflected radiation with a radiation receiver. Step four calls for determining a count rate of the reflected radiation and a change of the count rate with a processor, where the change corresponds to the hidden edge. The last step provides for associating the change of the count rate with a position on the workpiece surface. More specifically, the method calls for determining a position of a centroid associated with the change of the count rate, the position of the centroid corresponding to the position on the workpiece surface.
A technical advantage of the present invention is that it conveniently and effectively detects hidden edges. The system detects hidden edges by directing radiation towards an object with hidden edges, detecting the reflected radiation, and associating the reflected radiation with the position of the hidden edges. The system is compact and accesses only one surface of the object, and does not require contact with that surface. Another technical advantage of the present inventions is that it can detect hidden edges in different types of objects. The object to be measured may comprise a wide variety of materials, and does not need to be conductive. Additionally, the object may comprise different components, and may have air gaps in between the components. Another technical advantage of the present invention is that it provides real-time detection of hidden edges. The system only needs to perform a single scan proximate to the hidden edge to detect the hidden edge. In addition, the system does not require initial measurements to generate calibration curves in order to compute in real-time the location of the hidden edges. Consequently, the present invention allows for convenient and effective real-time detection of hidden edges in a variety of objects.